How to approach negative thoughts

I’m a bit confused about how to deal with negative thoughts. On one hand the app suggests I shouldn’t allow the thoughts to have real meaning or weight and that I should acknowledge them but allow them to pass without getting caught up by them. Yet in other exercises on this app we are told to challenge the thoughts by looking at what evidence the negative thoughts are based in and argue it the evidence against that. Should this challenging of the thoughts only be done as an occasional exercise and on a daily basis I should simply allow the thoughts to pass?