John:
Welcome to Ireland Reaching Out!
Unfortunately finding RC parish records pre 1840 in Co. Donegal is very difficult. I tried searching on Roots Ireland but no baptismal records came up for a Dominick Coyle in the 1830s (the earliest was 1870).
I did find some potential leads on the Titje listings.from the 1820s. Hopefull, the link below works. There was a Cormick Coyle in Ruskey townland in Raymoghy civil parish on the east side of Donegal and another Cormick Coyle in Ballyboes townland in Raymunterdoney parish in the northwest of Donegal. No way to know if either record pertains to your ancestor without more confirming data. http://titheapplotmentbooks.nationalarchives.ie/search/tab/results.jsp?…
I would add Dominick's story to our XO Chronicles site https://www.irelandxo.com/ireland-xo/history-and-genealogy/ancestor-dat…
Also, I would look into DNA testing. An autosomal test is probably the best since it will track your maternal and paternal lines and identify matches. You also can take the Y-DNA test since your are a Coyle. The Y test tracks your pure paternal line. However, the test is more expensive and goes back 200 years in my own experience.
Roger McDonnell