If you're in a script, touch the left-pointing Back arrow at the upper left) to get to the Scripts List page:
If you're on the Scripts List page, touch the Application Settings icon at the upper left:
If it's not on, toggle the spellcheck on:
Return to the script by touching Done at the upper right.
When a word is flagged as misspelled, it will have a dotted red line under it:
Touch the word and spelling choices will appear:
Touch the correctly-spelled word, the word will be inserted and the spellcheck bar will disappear.