You can set up buying orders on exchange manually, and wait. I don't think we actually need DCA service or bot for this investment approach.
Manual purchase may be the easiest solution, but it requires that emotions intervene and therefore will affect your decisions. For example, if you think that tomorrow the price of Bitcoin will be cheaper, you will sell now and vice versa.
Unfortunately, when people lose, they withdraw all their money, and therefore greed and fear are the biggest threat to trading withered.
The automatic DCA forces you to save and the amounts will be deducted directly from your account.