How to make iPhone or iPad print to letter size paper

Presumably you are attempting to print to an AirPrint-enabled printer. If so, your printer will advertise its print capabilities - including page formatting, print quality and paper size. If your printer supports multiple paper sizes, you should be able to select Letter or A4 (amongst others) when you select Print from the iPad.

Depending upon your printer, you may need to set your printer’s own configuration settings for the loaded paper type.

AirDrop and AirPrint are entirely different services. AirDrop is for transferring files or photos directly to another device that is in close proximity; AirPrint is Apple’s driverless printing system that works with AirPrint-enabled printers.

• Use AirPrint to print from your iPhone or iPad - Apple Support
• Connect an AirPrint printer to a Wi-Fi network - Apple Support

Apple AirPrint is a driverless connection protocol. A high proportion of modern printers intended for Home, SoHo and Business environments now support AirPrint. Check your printer model against this list:

About AirPrint - Apple Support

If your printer is not compatible with AirPrint, there are alternatives…

Some printer manufacturers have a suitable companion App that provides Print capabilities for mobile devices, often using a web-based print service. Others can print directly if the App supports other network printing protocols. By example, many HP Printers use the HP Smart App - available in the App Store:

https://apps.apple.com/gb/app/hp-smart/id469284907

No Buck2Fix, you are not kinda dumb, I'm pretty savvy and I'm having a similar problem - two similar iPhones, will only AirPrint in 3.5 inch x 5inch glossy paper size - I can go into the media options and get a blue tick on "Plain Paper" but it still prints 3.5 x 5