You needs to download and install SKEDit: Auto scheduling app from Google Play store.
After downloading launch the app, you need to create an account which you can even sign in with your Facebook account.
After logging into your account, tap on either ‘WhatsApp Business’ or ‘WhatsApp’ icon.
The app will prompt a query requesting ‘accessibility’ permission.
If you want to scheduling WhatsApp messages, you also get the option to schedule the post on Facebook, a text message, an email or a call.
After granting the app permission to access data.
you can easily create and schedule a post or a message by selecting a date and time in your Android phone.
SKEDit will automatically share or message without an user action.
There is also an option that will help you to repeat a message if needed.
You can also set a scheduled reminder instead of an automatic submission.