How do I fix this ID glitch?

Most of the time, when you upload a shirt, the shirt image's ID is 1 less, but if multiple people created assets at around the same time, it could have an earlier ID. Keep on subtracting 1 until you find it.

If you want to do this automatically in a game, you can use MarketplaceService's GetProductInfo method to iterate backwards until you find it.

local MarketplaceService = game:GetService("MarketplaceService")
local ShirtID = 114883953
local CreatorName = MarketplaceService :GetProductInfo(ShirtID).Creator.Name
local ImageID = nil

for i = 1, 20 do
	local info = MarketplaceService :GetProductInfo(ShirtID - i)
	print(info.Name)
	if (info and info.Creator.Name == CreatorName) then
		ImageID = ShirtID - i
		break
	end
end

if (ImageID == nil) then
	print("Image not found for Shirt")
else
	print("Found ImageID")
end

Note: This will not work with Group shirts, because the image was uploaded by a user but the shirt is owned by the group.