Just to clarify, are you asking for Metatron’s help? Or are you saying he is the one attacking you?
If you have a copy of the book Archangels of Magick you can use the rituals from that book to contact him (petition or evocation).
If not, you can open Metatron’s seal, or simply look up his name in Hebrew (the six- or seven-letter variant, doesn’t matter), or search online for an image of Metatron’s Cube, and open it as you would a sigil: take a screenshot of it/print it/ draw it, and then open the seal by relaxing your gaze and looking “through” the image until it begins to flash (e.g. the seal might appear to move, double up, lines disappear/reappear).
If you don’t have the book AoM or any previous experience contacting spirits then you can probably adapt the below ritual:
Metatron does not have an enn (that’s a demons-only thing) so you could simply repeat or chant his name instead. But at the bare bones, you can open his seal and chant his name to call on him.
Ask an entity you trust, or try a divination (pendulum, tarot cards), if you have any suspected names of entities. Otherwise you may need to do some other ritual, like asking for a secret to be revealed to you/to learn hidden knowledge, and wait for the answer to come by intuition or coincidence.
Despite what I said above, a banishing ritual isn’t necessarily like a bouncer throwing someone (everyone) out of a club. It’s more like having a bodyguard. It’s about protecting yourself and your space. You can specify that you invite certain entities to stay around if they wish to.
You might want to look at this thread:
And summon the servitor Luna, to ask her to protect you and your space. She will allow in only the entities that you wish to be in your space, so if you call her and specify that she should remove harmful energies only, you should be good.
If you want to banish Metatron from your space then try Luna, and/or the basic LBRP, and firmly but respectfully ask him to leave.
Apologies if this comes across as too basic, I’m not sure of your experience so just trying to give you a few options to try. Good luck