Starting in Doneit 2.6, you can now upgrade your monthly or yearly subscription to a lifetime one in the settings of the app. Simply tap on the ‘Upgrade to Lifetime’ button located under the ‘Doneit Premium’ section in the settings of the app. Please just note that after upgrading you will still have to cancel your monthly or yearly subscription manually. You can do this directly in the app on iOS and iPadOS, or in the settings of your device on macOS by searching for the ‘Media & Purchases’ option and then clicking on the ‘Manage…’ button next to the ‘Subscriptions’ title.
If you would like to upgrade your monthly or yearly subscription to a lifetime one prior to Doneit 2.6 update, you will have to wait until your current subscription expires and then you will be able to purchase a lifetime option on the purchase screen in the app.