Once the high resolution photos are in iCloud how do I get them back onto my iPad or iPhone if I want to send them or print the high resolution version?

The photos are being saved in iCloud and will stay on your phone as well, even if in "optimised" mode.

Taping onto an optimised photo will download the original quality from iCloud onto your device, and you will be able to share or print it.

Check this article:

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Download photos and videos from your iPhone, iPad, or iPod touch

1. Open the Photos app, then select one or more photos or videos. 
2. Tap the share button .
3. Tap AirDrop, then select the device that you want to share with. Learn more about using AirDrop.

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copied from: Set up and use iCloud Photos - Apple Support

I ran out of storage so all my photos look grainy on my iPhone due to the ‘optimise storage’’ setting I didn’t realise I had on, I have now bought more storage and changed the setting but all my photos are still grainey and my videos won’t play on my phone.. nothing happens if I tap them? They just stay grainey 😩😩 helpp

@Meg6657

Did you try to download the photos onto your computer?

This article explains how to do that:

Archive or make copies of the information you store in iCloud - Apple Support