STEP 1
Go to your Shopify Admin Dashboard, and click on Products.
STEP 2
Select a product from the list.
STEP 3
Click on the Show HTML icon.
STEP 4
Remove unwanted formatting or add to the code.
STEP 5
Click Save to apply the changes.
Alternative Method
Copy all content from the product description show HTML and paste it on a notepad and copy it again from notepad and paste it to the text editor. This also clears formatting.