Here's a good beginner tutorial for that sort of thing
There's also this on the Vocaloid Wiki
https://vocaloid.fandom.com/wiki/English_-_Japanese#Japanese_to_English
A few other things:
-some JP UTAUs may have extras for other languages/have individual quirks that make them easier or harder to use in English. It's a good idea to check the read me, or even scroll through the oto.ini looking for samples--sometimes the results can be surprising!
-Some UTAUs I find using う or w as a substitute for English r (especially with positive gender flags) can sound better than using Japanese r.
-You don't have to put every consonant in there every time. Sing it to yourself/listen to the original and listen to what consonants get "dropped," like the "t" in "want to" getting dropped to make the word "wanna"
-The "er" vowel is a pain in the behind to approximate no matter what and there really is no good solution
Good luck!