Use the elevator to the top and then follow the corridor into the tower. Make a detour to the ladder and open the gate at the top. It's an option to get back to Elden Ring Runes the final site of grace. There's a blackflame monk across the hallway who has the perfect posture and terrifying incantations But he shouldn't pose too much of a threat.
At the end of the hall, jump onto the ledge on your left and continue following the path around the tower until you're immediately above another strut with a crack. Just like the first one, it may break and you're instructed to stay alive. There is no other path to the base of the tower. the strut did fail out and it killed me twice, and did no damage a third time. If this happens to you, keep returning via the shortcut and attempt the leap until you land in a safe spot next to the elevator. You can ride it down to another site of grace, and past another blackflame monk to find the main entrance for the Godskin Apostle.
Most of the Apostle's actions are pretty well-telegraphed. you shouldn't need many attempts to find his rhythm. One thing that made me uncomfortable was an attack where he quickly spins his blade front of him like an industrial fan, holding the blade in place and then walking forward for a massive blow. I never managed to block him out during the attack, so it's safer to stay at a distance until it's over. Be wary of buy elden ring weapons when you heal, too. The Godskin Apostle is known to spit in a blackflame missile at you while you are trying to drink off your glass.