How do I soften clothes hardened by modge podge and glitter?

Mod podge is not meant to be used on fabric than needs to remain flexible enough to be worn as clothing.

Neither is craft glitter meant to be used on clothing, as it does not stay affixed when the fabric moves, or when the garment is washed.

Mod podge and standard craft glitter were the incorrect products to use. Hop and bop over to you fabric or craft and hobby shop. Check out the lines of fabric glitter that are formulated to be washed.

https://youtu.be/2lVildSDsHM

https://youtu.be/IL4oJONgDu4

https://www.glittermyworld.com/glitter-t-shirts.html

https://www.marthastewart.com/992939/how-stencil-t-shirts-glitter

I've never done this and I'm not very crafty, but I might try mixing a little glitter in regular (clear?) fabric paint. I'm not sure, but I think there is glittered fabric paint on the market. Sometimes we waste more money trying to make our own products with the intention of saving money and end up with little experiments that failed. Did you know that cotton fabrics and synthetic fabrics each have their own dye product made by the same maker? I just found that out, and am so glad that I never ruined any clothing learning that lesson. Don't give up, arts and crafts are meant to be enjoyable, not hassles.

You could try soaking the clothing in rubbing alcohol to get the Mod

Podge out. I know it works for brushes. And as previously stated by others, you need to use products that are specifically made for fabric and to read the labels on the products for fabric content (what percentage cotton, etc.) to get the best adhesion. Decoart makes two products for clothing - SoSoft fabric paint and Stylin paint. Stylin can be used on leather, plastic and some fabrics that doesn't crack. SoSoft is a fabric paint that remains pliable. Hope this helps.

Try reaching out to the manufacturers, see if they have any suggestions or find craft groups online that may offer tips.