You probably need to clean the print heads, as your post suggests that they've become clogged. (That tends to happen a lot in warm weather, so it's not particularly surprising).
The way to access the head cleaning option varies across different makes and models of printers but the following generic method should get you there with any printer. (NB: I'm assuming that you're using Windows 10. Things are a bit different with earlier versions of Windows):
Click the Start button.
Click the Settings (cogwheel) icon.
Click Devices.
Click Printers and Scanners.
Click on your printer model.
Click Manage.
Click Printer Properties.
Click on the Maintenance tab (or similar - that bit might vary between printers).
Look for a button labelled 'Cleaning', 'Clean Print Head' or similar. Click on it.
Once the cleaning routine has ended, click on the option to print a test sheet. If it prints out correctly, close the window because you've finished. If it doesn't, try the cleaning cycle again. (If you're still getting nowhere, look to see if there's a 'Deep Clean' option and give that a go. In really bad cases of head-clogging, I've sometimes had to run 'Deep Clean' half a dozen times or so).