I would like to install more RAM into my iMac 2019

Memory in that iMac is not user accessible and will require near total teardown of the computer to access.

Please see:

Install memory in an iMac - Apple Support

❝3. Memory is not removable by users on iMac (21.5-inch, Late 2012), iMac (21.5-inch, Late 2013), iMac (21.5-inch, Mid 2014), iMac (21.5-inch, 2017), iMac (Retina 4K, 21.5-inch, 2017), and iMac (Retina 4K, 21.5-inch, 2019). If the memory in one of these computers needs repair service, contact an Apple Retail Store or Apple Authorized Service Provider. If you’d like to upgrade the memory in one of these models, an Apple Authorized Service Provider can help. Before you schedule an appointment, confirm that the specific Apple Authorized Service Provider offers memory upgrade services.❞ - from the above linked Apple Support document.

If you'd like to see installation videos about the process on that iMac, please see:

Upgrade/Install Memory in a 21.5-inch iMac (2019) - macsales.com

You can look for Apple authorized service locations at this link:

https://getsupport.apple.com/repair-locations?locale=en_US

You can't do that yourself. Contact an authorized service provider.

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