Some makeup manufacturers have some kind of guides for that. But most importantly you need to figure out if you have a cool, warm or neutral skintone. And then find a shade that is made for that tone and matches your skin colour.

A tip I’ve seen - but not tried - is picking a light and dark shade and mix them until they match your tone.

Depending on how bad your beard is you might want to get some camouflage makeup (I certainly meed that…).

Sephora helped me when I had a full fledged beard. See if there’s one near you. Some even have a skin color imaging gun to help find a proper foundation shade.
Not sure about apps, but if it uses an image to find certain shades and/or colors, make sure you have good lighting

There are some stores that are noted for being CD-friendly: M.A.C., Ulta, Nordstroms

You also want to look for a local CD group. This page listing active support groups at the time has been down since 2021, but it’s still the best out there. https://web.archive.org/web/20210518050654/http://www.abgender.com/support.htm

They’ll know all the “safe” local places, but most importantly is being able to socialize and not feel like you’re alone.

edit: Aha! I just found this directory that looks like it’s maintained https://tgguide.com/transgender-support-groups/