There is no reset button. 

In any case, before continuing with any approach either suggested here or found anywhere else: create a backup of your database so you can roll back in case anything goes wrong! Furthermore, I'd like to highly suggest to perform the action mentioned below in a test or staging environment first to see and test the whole result prior to doing so in your live system.

As its completely unspecified what your issue with eCommerce is, below are three options listed that may help you. Note that 1) is the approach with the HIGHEST impact on your database, yet it should perform the 'reset' you're asking for. However, whether or not you actually need such a 'reset' depends on what is going on in your database right now. Therefore, you may try option 3 first and see if it's working for you and work your way in inverse order up to the complete uninstall of eCommerce if you have to.

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1. You may try to simply uninstall and then re-install the eCommerce app (technical name website_sale). Upon hitting uninstall for any app you'll see a wizard window allowing you to Show All to see the full implication of performing the action prior to actually doing so:

Depending on your system, you will see different apps and modules that are going to be uninstalled along with eCommerce.

Note that EVERY selection directly specific to eCommerce is going to be removed (i.e. product categories, whether or not products are visible in the webshop, the definition of the webshop itself, ...).

In case previously performed changes are going further then just eCommerce, you may have to uninstall the Website (technical name website) app as well. This will have even further implication on your database and will erase all content added to your website. Hence, HANDLE WITH CARE!

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2. A less intrusive way could be to just create a new Website in Settings -> Website -> Settings of Website --> + New Website, set it up to your liking and deactivate the already existing one. Whether or not this approach works for you depends highly on why you're facing issues in your current website already.

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3. Furthermore, you may try to simply change the theme of your current website, in case the issue lays simply within the theme. You can do so from the website Editor -> Edit -> THEME -> Theme: Switch Theme:

Hi

To reset the eCommerce (Website Sale) module in Odoo, especially after a developer made changes externally (e.g., via custom code or directly modifying views), follow these steps to cleanly reset the module.

Note: Backup your database first — resetting or uninstalling can delete or break data.

Step 1: Activate Developer Mode

     Settings > Activate Developer Mode

Step 2: Uninstall Website Sale

Hope it helps