The increment arrows are inherent in <input type="number">, your browser automatically adds them.
When you’re setting up your form you just use the ‘number’ input rather than a ‘text’ input.
So instead of <input type="text" id="field_id" name="field_name" value="" />, what you want to use is something akin to:
<input type="number" id="field_id" name="field_name" value="" step="1"/>
You can see the various attributes that can be set/specified for number inputs here: