When you are in the settings for the Co:Writer Universal  iOS app there are two tabs to set the Font settings one for Word Prediction the other for text.

Steps:

1.  Click on the Cog icon on the top of your composing page. ( Word Prediction should be in Bold)

2. Adjust your guess settings.

3. Click on the grayed out word Text to the right of Word Prediction.

4. Adjust your documents Text and Font settings.