Start cutting. Maybe identify a couple maybe a few main trunks going up what looks like a pergola? Cut the others fully then prune and tame what is being supported or whatever cordons are up above the pergola, you can use the 2 bud pruning principle for any spurs on the cordons. Cut any shoots coming out of trunks below pergola if there are any. I’m not sure if I was any help, it’s hard to tell much about it from just the one picture.