Indeed, your current text reads like a diary, which might actually not be a very bad thing, since it is a report of your actions. Still, in general, it's good to remember that we are writing for our readers, and your choice of words actually conveys some message to them. In particular, the use of "I" indicates that we are dealing with your personal observation / opinion / design, and for some reason you feel important to emphasize it.
The following is my rough revision of your fragment.
"For the health belief model I had to discover four specific points1: perceived susceptibility, perceived severity, perceived benefits and perceived barriers. Since people are not very open when talking about covid2, questions should be asked carefully3. I used the following procedure4: First, the respondents rate the severity of each point from 1 to 5. After answering all the questions, the respondents have to justify their answers. This approach results in more truthful answers4."
- Or "...it is necessary to discover" -- depending on whether you had to do it due to some specific design of your experiment, or it is a general statement, valid for any health belief model.
- This is a general statement, so it is probably not imprortant for the reader whether you personally noticed that or somebody else (but in the latter case it would be good to provide a reference to literature).
- Same as above: you are actually making a general statement: it's not just you have to be careful, it applies to anyone trying to do it.
- If you want to get rid of "I" in such cases, use passive voice: "the following procedure was used". Personally I don't like passive voice, but it's okay if used sparingly.
- Same as above: your method is supposed to work better for everyone, not just you; so it isn't giving you more truthful answers, it would work for others as well.