>>45485132I will suppose you already have PkHeX and a pk8 file. If not, sending the mon to a sysbot/seedchecker bot who will send you the file is an easy way to have it.
Once you opened PkHeX and that file, to change the OT and ID, you have to go in the "OT/Misc" tab, which should be the last one, and change them in the "Trainer Information" frame. To change the Ribbons, look down and click the Ribbons option where you can choose the right Ribbons for it (the Classic Ribbon is just called Classic and is at the C letter if you go a little down).
To change its location, go in the "Met" tab, which is the second tab, and change the "Origin Game" to the right one and the "Met Location" to the one you want (I suppose you will want to make it from Ultra Sun and put "the Alola region" as the location if it's the Entei I'm thinking of). To change the date, still here, just change the "Met Date" option to the desired date. The "Fateful Encounter" flag is just under so make sure it's also checked if you want it to be truly an event mon.
If you need anything else, ask away. It's not really hard, you just need to take your time the first time you do it to avoid doing mistakes or forget details.
