How to kosher glass heat mats that have been mixed together
You can kasher them by pouring boiling water over them. they should be washing well so that there is no grease dirt etc. on them, then pour boiling water over them and then rinse them in cold water.
The reason is because there is controversy if according to the opinion of the Rema if glass needs kashering or if it can not be kashered at all. In this case it isn’t even clear that the mats were indeed milchig or fleishig, because the pots are usually clean. Even if one of the pots wee once dirty and were placed on to the mats when hot, nevertheless the main use of the pot is not in away that it will become really meaty or milky. therefore even according to those who go according to the stringent view, it would suffice to kasher it with iruiy kli rishon.