In order to assign all products to the website please, go to your Magento 2 Admin panel > Catalog > Product and Select All products.

Magento 2 select all products in the product grid

Then, choose Update Attributes in the Actions select box.

Update product attributes in Magento 2

Afterwards, move to the Product Information > Websites and in the Add Product to Websites section, choose the website you need.

Assign all products to the website in Magento 2

Next, press the Save button.

Magento 2 update product attribute

Wait some time. After a while, you'll see the notification about the assignation being performed.

Magento 2 result of product attribute update