Ok, in that case: who Is your email provider, and are you using Android or iOS? Because in iOS its not below, but on the right side of the screen, but in your case it sounds like your provider has not activated that feature in which case you won't be able to add a second account.
to add a second account to your Mail App, tap on the hamburger menu on the upper left side (three horizontal lines). Below your avatar you find a plus-sign. There you can add another account.
Hope I could help.
there is no plus sign below my aviator
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