HODL. There are a lot of lending platforms but that would require you to have a fixed contract duration between which you won't have any control over your altcoins or some platforms would require you to convert your altcoins into their coins and then lend their coins in order to use their lending platform. Both the scenarios are useless as the altcoins you have might be the ones which you have invested your lot of time in order to know everything about it before investing and if you convert it into another coin for just growing your wealth it could be a possibility that your old coin might rise in the future and the converted ones are as it is or worse, have fallen. So just hold you altcoin and let them be dead in your wallet.