I've modelling a pouch with some liquid inside. The liquid has surfaces on the front, back, and the bottom, and I'm trying to put a surface on the top so that I can knit it together. However, I'm not sure how to proceed with this.
I've attached a pic
You might want to investigate the intersect tool. SOLIDWORKS - Basics of the Intersect Tool - YouTube
And you might also want to check out some the ways that it was done here:
The 10th Weekly Power-User Challenge (September 15th, 2017): Measuring Wine Carafe
without seeing your model, it's hard to help. Can you post your part here?