You can create a new conversation named - UNSET variables.
For retesting the bot, you can create a new conversation for unsetting all customer properties.

You can follow the below steps:

1. Create a new conversation and add a trigger keyword ‘resetvar’
2. Use Set Property blocks and set each property equal to *UNSET* to reset the properties. Add Set Property blocks for all properties that need to be cleared.
3. Use ‘Jump to other conversation’ block to jump to the starting conversation. Now for retesting the bot, you can simply type ‘resetvar’ on the WhatsApp bot which triggers this conversation and all the customer properties will be reset and flow will be transferred to the Starting conversation.