For other PS players..
1.) When wyrm's energy ball is near you pres [R2]
2.) When you get near wyrm's body and some segement is highlighted then pres [R2]
3.) Then press [X] to jump off, move view to wyrm's head direction, highlight next segment, press [R2]
4.) When you are near wyrm's head, you can press [ ▭ ] to control the wyrm
5.) Approach towers, pres [R2] to destroy them with fire
6.) Go through portal, maybe you need [L1] and [X] to change wyrm's altitude.
- wyrm's energy balls are sometimes not precise and they don't go directly towards you BUT fire [R2] anyway wyrm's direction (otherwise you could be knocked off the horse)
- it happened many times that I wasn't able to control wyrm [ ▭ ] because other player was a little bit faster
- sometimes you are lucky, worm's fly your direction and you jump to head much sooner
- if wyrm is right above you I suggest to teleport/run further away and start flying on him from distance (He was firing balls on my from above I was not able to see/target them at all)