A fiduciary must make investment decisions based on the best interests and needs of their client as opposed to one that may pay them a higher commission. It also means that this person must avoid any possible conflicts of interest.
You can often check online to see if an individual or investment company identifies themselves as a fiduciary.
Reach out to friends and family members who may invest to find out who they work with. Getting a personal recommendation from a trusted source may help you may a decision with more confidence. You can also use the Securities and Exchange Commission Adviser Database (SEC) website as they are the governing US body that regulates this type of industry.