- Edited
Since you have not written anything else, I assume that you are using the pre-installed standard keyboard.
I can think of at least two ways in which the keyboard supports spelling correction:
1.) Settings> System> Keyboard> On-Screen Keyboard> Keyboard> Text correction> Auto correction.
If this setting is toggled on, the keyboard corrects supposed errors.
If you deactivate it and activate the show corrections suggestions
toggle instead, the suggestions are displayed above the keyboard (if you activate both it shows the suggestion and autocorrects it).
2.) Settings> System> Keyboard> On-Screen Keyboard> Spell Checker
If the spell checker is activated, it underlines spelling mistakes in red.
If you change these settings, it can sometimes take a moment for them to take effect - at least that's the case for me.