Hopefully you’ve been successful with your Autumn varroa treatments and your hives have low numbers. Best way to check is to take a sample of 300 bees and test for varroa using either icing sugar or alcohol. Divide varroa count by 3 to get a percentage. If over 2-3% you need to treat. Refer to this article for a useful table. https://honeybeehealthcoalition.org/wp-content/uploads/2015/08/HBHC-Guide_Varroa-Interactive-PDF.pdf
It also has a good explanation of testing and control methods. You’ll need to collect your bees for sampling on a warm day.
If you suspect that your treatment may have been ineffective due to varroa resistance, here are a couple of ways to check http://www.fedfarm.org.nz/Files/VarroaResistanceBrochure.pdf