How about constructing "as promised"? As in "As promised, I will come see you in April". "Kom mwen te pwomes, m'a va vini pou we ou nan Avril" maybe?

you're very close :)

As promised → kòm pwomi, kòm mwen te pwomèt

"As promised, I will come see you in April".
"Kòm mwen te pwomèt, m'a va vin wè w nan mwa avril"
or
"Kòm mwen te pwomèt m'a va vin wè w an Avril.

and, I thought you might be interested to know this popular Haitian proverb about pwomès. You may have heard it already:
In Haiti, we say Pwomès se dèt → Promises are debts.

kenbe la.

Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words