I found the DIM folder but it doesn't have a downloads folder in it?
Also... a lot of the assets come in .RAR not in zip files. Tried it with .rars and nothing popped up to be installed.
Open up Daz Install Manager and click on the "gear" button in the upper right. Select the "Downloads" tab. The "Download To" item right at the top will give the directory that
(a) Daz Install Manager would download content into, if you download content from the Daz Store
(b) Daz Install Manager will install from.
Thus, if you put properly-formatted DIM zip files in that directory, and _then_ launch DIM, it should see them.
DIM won't install RAR's - they have to be the IM000XXXXX-XX_XXXXXX.zip files that come from the Daz store.
Also, if you have something already installed, DIM will drop it from the list of things to be installed.
You can also choose to have DIM remove the ZIP files after it's done the installation - I usually do that, since I keep copies of all my ZIP files elsewhere.
RAR files have to be manually decompressed. If they have DIM files inside them, you can install those as above. If they have raw content folders, then you have to install that content manually by copying it into the DAZ folder structure.