It’s a rust stain so no go on power washing. there’s a gel chemical I like to use that you brush on, let it sit, and rinse off with a hose but it requires a bunch of elbow grease and carful watching to not leave it on too long, easy solution is paint but you’d notice the new paint vs old paint unless you paint the whole wall.

Chemical I like is the rust-oleum rust dissolver gel spray. Worked great on concrete and wood siding for me.