Can hagalah be made on a swiss army knife? As well how should it be tovelled?
A swiss army knife only requires tevilah if its prominent use is for food-related purposes; if it is generally used for other things, but sometimes for food, it does not require tevilah.
Assuming that it requires tevilah, it can be immersed in the regular manner (opening the knife, and then immersing).
The same applies for hag’alah: the knife should be opened, cleaned, and immersed into boiling water.
Best wishes for a chag kasher ve-same’ach.