Hi @mosaeed,
if you click on Next here, you should come to the following screenshot, where you can click on the radio button Show original error...:
Now I marked org.knime.dl, which is provided by the normal KNIME Analytics Platform update site: in KNIME Analytics Platform Installation Guide you see the link to the zipped update site: https://update.knime.org/analytics-platform/UpdateSite_latest51.zip
Download that, make it available, then you should be able to install it.
Does it work?
Best regards
Steffen