ᐅ Waterproofing in the bathroom: floor joint is coming loose.

Hello forum,

We have a walk-in shower in our bathroom. The seal at the waterproofing layer is now coming loose (see photos).
Can this sealant be simply replaced, or is there something special we should be aware of? Would it be better to call a professional?
I attached several photos because the affected area is hard to see clearly in the pictures.