Curious if there is a way to adjust the trash folder setting? I cannot find how to adjust the setting to hold trash emails for a longer period of time.

My H's work phone seems to dump the trash folder every couple of days. When I do manage to check the trash folder, it shows emails for a split second and then most disappear. Wondering if there is a setting I can adjust? If so, I would appreciate being walked through how to change this setting. Thank you.