Mask-approaches isnt too different. Of course you cannot say she is pretty, however you can comment on other things that are not covered by the mask. E.g. I like your style, I like the way you walk etc these are basic openers. Of course, expand it and make it more personal when talking to a girl e.g. I like the way you walk, you look like you are on a mission or something today (of course if she is walking fast). In terms of face, it is going to be difficult but that is a risk you have take unfortunately. You can always get her number/social media and look at her there to confirm. If she is not your type, dont text her and move on. It is still good experience to approach.