Hello, in the Dell documentation it says Two M.2 2230/2280 card slots for SSDs[br]
You can find the documentation here with this information on page 13 : [link|https://dl.dell.com/content/manual39657475-dell-g15-5510-setup-and-specifications.pdf?language=en-us|Dell G15 5510 Manual|new_window=true][br]
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The procedure for adding a second disk is on page 17 of the [link|https://dl.dell.com/topicspdf/g-series-15-5510-laptop_service-manual_en-us.pdf|service manual|new_window=true]