After adding a new offer price to a course it cannot be changed. This is because price history is needed for reporting purposes. Students may have already purchased your course using the offer price or there could be active student subscriptions using the price.
If you need to make a price change, create a new price and set it as the default. Then disable the old price.
The screenshots below show an example of a subscription price increase. The same steps apply to one-time pricing.
First add the new price and then click the small gear icon next to it and choose: Make Default.
Then click the small gear icon next to the old price and choose: Disable Price so it can't be used going forward.
Please note: Students who already purchased your course with an old (now disabled) offer price won't be affected. They'll still have access to course content and prior sales reports will remain accurate. Disabling a subscription price won't affect any existing subscriptions using it. They will continue to bill using the original offer price. You can still view your disabled prices by clicking Show disabled prices on the Course Pricing screen (see below)