To get a thumbnail of the asset you can do something like this within a script:
local imageLabel = script.Parent -- Assuming that the script is inside an ImageLabel.
local assetId = 0 -- AssetId of the asset you want to display.
imageLabel.Image = "rbxthumb://type=Asset&id=" .. assetId .. "&w=420&h=420"
For more information on rbxthumb you can check out this post by TheGamer101.
Hope this helped!