Newbie User Researchers query: How to probe for solutions to "Trust" issues with a Fintech app

I am seeking tips from more experienced researchers, please. I am a graduate who has been given a research challenge for an intern interview. The task is as follows:

If there is low signup for a new (fictitious) investment app due to an identified lack of trust, what user research methods should one consider in order to probe this area and uncover insights?

I am simply to give a few recommendations as bullet points.

Might anyone have any suggestions here? I have spent a great deal of time thinking and reading and cannot come up with anything solid, so your help is much appreciated.