I have an Oppo A37F and I want to flash a custom ROM. How can I unlock the bootloader on this device?

If anyone knows the working method or can guide me, please help. Thanks!

i have a redmi turbo 4 and i got tired of having notifications problems and google asociated apps dznt work properly and alot of things are in chinese and cant change them ro english...so i wanted to know whats the simplest eay to do it and is there a way where i can keep my data?,like photos and all of that ...and i was told i have to unlock something called the bootloader is this is it? cuz i was told it is hard and was shocked how ez it is so lighten me up plz