Thank you for reaching out to us.
The patch needs to be removed for immersion, and any remnants of the glue should be scrubbed off. You should ask your physician whether you can reapply the same patch after mikveh, or whether you need to use a new patch. It is often acceptable to reapply the same patch if the adhesive still works well. The package insert will probably give some guidance on this.
You can also ask your physician whether the patch can be left on for 60 hours instead of 48. This would give you more flexibility with scheduling. For example, you might be able to change the patch at night when you go to mikveh.
You might also find it helpful to arrange a free, personal consultation with a Yoetzet Halacha Fertility Counselor, details here.
Please feel free to get back to us with any further questions.
We wish you much hatzlacha in your fertility treatments!