Apply a rig arms-extended to a mesh no-arms-extended

I just downloaded a nice armature animated form the Mixano website. I want to apply it to a character I modeled.
My character is modeled in a natural rest position, with his arms lowered and his hands at the height of the hips, but seems that the rest position for the Mixano armature is the typical arms extended horizontally.
When I edit the armature to adjust the size and position of the bones to my character, and go back to the posing view it results in a weird flexion of the arms.
Let me know if I didnt explain myself properly. How should I proceed to apply this armature? thanks in advance !

Try this: After you move the armature bones to match the model (in edit mode), switch back to pose mode, pose menu> apply> apply pose as rest pose. See if that works.

Applying the rig while the arms are by the character’s sides may lead to some weight-painting nightmares.

If you instead repose the arms to match the armature’s rest pose, the only thing you’ll have to redo from scratch will be the shoulders. And technically, only one shoulder since you’ll mirror it across.

And it might take far less time considering that you’re unfamiliar with the rig and (I’m assuming) how rigs in general are built, applied, etc.