Jim is correct. You have a capillary flow restrictor there.

Are you replacing your current membrane with a membrane of a different capacity?

If no, then probably no need to change your existing flow restrictor - just leave it in place.
If yes, then the following should help:

Locate your waste water tube, specifically where the tube attaches to your RO membrane housing at a fitting. Remove the tube from the fitting and look INSIDE the end of the tube, and if you currrently have a capillary flow restrictor - that's where you'll likely find it. If it is not there it is elsewhere in the WASTE tube.

Pull the old FR out, insert the new one, reattache the tube to the waste port fitting, and you are good to go.