How do i merge a moveable part of an object? i'm quite new with blender, so pardon me if this question is trivial.

I'm trying to import this model to vrchat and realize that the pauldron part is actually separate despite being the same object.

So, i don't need it to move separately and want to make it merged as one. How can i do it?[![enter image description here][1]][1]

Edit:
i'm sure my words earlier made some confusion, what i meant is i want to make this part of the model to keep attaching when move. how can i do it?
https://cdn.discordapp.com/attachments/434777529677774869/622668359787479060/ezgif-1-ac95a637266d.gif
Are you talking about the bones being separate? Because you only have one object in your hierarchy.

If you're talking about the bones you can go into edit mode, select the ball on the end of each bone you want to connect and press F to create a new bone between them.