Any statements of general fact should be written using the present tense.
Any discussion about prior research should be explained using the past tense.
If the subject of your sentence is your study or the article you are writing (e.g. “Our study demonstrates…,” or “Here, we show…”), then you should use the present tense.
If you are stating a conclusion or an interpretation, use the present tense.
If the subject of your sentence is an actual result or observation (e.g. “Mice in Group B developed…”), you would use the past tense.
https://wordvice.com/which-tense-should-be-used-in-abstracts-past-or-present/
