Update a post’s acf field with rest API or Database

i want to update the value of an acf field in the post tried doing this with rest api but didn’t work, So now how can i possibly do this with the database?

this is how the json looks

{
id :37,
etc,
etc,
acf:{
mast_head : {
id :13,
post_content : “sregaerg”
}
}

}
i want to update the post content of the mast_head which is inside acf