Alteration suggestions- help! (tight arms)

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My last post gave lots of ideas, so I hope hive mind will be able to help again.
I got a lovely Lindy Bop dress, this time in the right size. It fits perfectly everywhere... but the sleeves. The fabric is a bit stretchy, but quite heavy, and the sleeves reach halfway between the shoulder and the elbow.
I can fit my arms through, but the sleeves are v e r y tight, and there is a bulge when the skins shows, you can tell the sleeves are tight. I could put something over them but it also hurts in long term to have arms squeezed like this.
If I take them to alterations, what could they do with it?If anything.

Need a picture

Dont have a photo of the actual dress but sleeves along the line of this but ending maybe 10cm above the elbow, so larger arms bulging out.

You could put a piece of fabric in the seem though would probably have to match. Or out a slit on the outside arm

That’s a tricky one. What’s the fit on the armhole like.

Ypi need a dart shaped piece of fabric inserted from the armhole to the end of the sleeve in the same colour on the underarm.

If the armhole is also tight, then you’ve got a much bigger problem!

Does the armscye need opening up or is it OK? If it needs opening, you can use the existing sleeve as a template for a bigger sleeve. If it's OK, then you just need to insert more fabric into the sleeve. Stretch lace fabric is what you need here.

Well, the arm goes through, but I think the whole bit that is under sleeve feels squiched, like if you wrapped a bandage too tight. So the 'outer arm hole' near the elbow is very tight, but not the whole the arm comes in where the armpit is, hope that makes sense?

Diagramme