How to make a portal spawn in a structure already on

Hi, I'm trying to make a structure that has a portal in it that I wan to be already on when found by a player, but I tried doing so and when I spawn the structure with the structure block the portal is off but it's crucial for the portal to be on for this mod, so is there any way I can do this?

PS: I have absolutely 0 knowledge about eventual procedures, so if you are going to explain how to do this with a procedure please be extra specific and maybe tell me where to find this exact procedure element or its specific name so that I can search it in the procedure search bar, cause otherwise, I'll have absolutely no idea of what to do cause I really don't know anything about them, all I've made so far in my mods was all stuff I could directly do in MCreator, sorry if this bothers you, I'm still a newbie.

Thanks in advance.

Edit: I think this was the wrong forum section, sorry I just realised it probably should've been in Modding (Java) but I can't change it anymore, please don't take this down