If you mean tabs for guitar chords, you can go to a website like ultimate-guitar.com then find a song you like. For example here is a link to 'Leaving on a Jet Plane by John Denver"
https://tabs.ultimate-guitar.com/tab/john-denver/leaving-on-a-jet-plane-chords-32979
at the bottom of the screen you will see a white box that reads
"FONT -1+1 CHORDS AUTOSCROLL TRANSPOSE -1 +1"
you can transpose the tabs to a key that is better suited to your dulcimer by clicking on the +1 to transpose it up a half step or the -1 to transpose it down a half step. For example if you found tabs in the key of E, but your dulcimer is tuned to D, you could click the '-1' button twice.
This chart might then help to translate the chords into dulcimer chords https://everythingdulcimer.com/tab/chord_chart_dad_major.pdf

I don't know of a way to directly convert the kind of tabs which show all 6 strings, other than to just convert those tabs into their notes, then convert those notes into dulcimer tabs. This can be quicker than you might think with a chart like this
As Lisa mentioned, your biggest obstacle at that point is the chromatic frets, which might not be a problem at all if your dulcimer has a lot of frets. Quite a lot of pop music is mostly diatonic so if you are willing to put in the time to translate the guitar tabs into their notes, then transpose those notes into a key you can play on your dulcimer, a lot of times its very rewarding, but sometimes it can be fruitless if you dont have the frets you need.
Hope this helps
-Nate

I much prefer classic ukulele tab chords such as here: https://www.ukulele-tabs.com/ukulele-tabs-chords.html call be old fashioned but it just reads easier for me.

updated by @endaamelia: 03/06/23 10:27:07AM

When you say "guitar tab" do you mean six-string note-by-note tablature?  Or are you looking at the leadsheets and chords-with-lyrics sheets that people on the internet call "tab"?  The chordsheets are no problem.  As Ken said, a G chord is a G chord.  We can explain more if that's what you're looking for.

Actual tablature is tricky.  It's not just that a guitar has 6 strings tuned different from a dulcimer.  It's the chromatic frets.  Unless your dulcimer is chromatic, you could figure out how to map every note on the tab to the corresponding note on dulcimer and still not be able to play it because you don't have frets in the right place. 

Look into tab software like TablEdit.  I think there's a way to enter guitar tab and convert it to standard notation.  Maybe there's a way to convert guitar tab to dulcimer tab.  Hopefully a TablEdit guru will check in here.

You might get somewhere with ukulele tab (4 strings) if you set your dulcimer up with 4 equi-distant strings and tune them DGBE. 

Another option, and perhaps the most fruitful one, is to buy all the dulcimer tab books you can find that have contemporary music (there are some).  After you've played enough tab, you'll get a better idea of how this works and you'll have more success at figuring songs out by ear. 

The only thing you can get from guitar "tab" is get the sequence of accompaniment chords, not melody chords.  A G chord is a G chord, a D chord is a D chord, regardless of instrument.

As far as I know, there is no way to convert guitar tab to dulcimer tab. I think most folks would start with the standard music notation [SMN] and write their own. Doing melody only is fairly easy if you have a little background [FACE, Every Good Boy Does Fine] and know the basics of your MD [tuning, note locations], adding chords [fingerings] etc is harder. Some use a music notation program like TablEdit, MuseScore, or Finale etc. 

I've seen old posts about how to do this. I really want to play more contemporary pieces, but need to know how to figure it out. I have played with plunking around by ear but not much luck. There has to be a better way.