Swap is not part of the Solana app. On a Solana session there is no Swap button in the Account popover, no Swap tab in the transfer dialog and no swap page, and with no wallet connected the tab is not offered at all.
Convert assets in your own Solana wallet, then open the Account popover from the wallet button in the header and use Fund to bring the asset you want into your Nolus account. Fund and Withdraw are the app’s asset-movement tools. See Fund & Withdraw Assets.