Step 1: From your Shopify admin, click "Products" on the left menu, then click on "Inventory".
Step 2: Filter the products that you want to edit using the search bar.
For example, you can type "watch" and all the products relevant to the search will be displayed on the page.
Step 3: Click on the check box at the top (to the left of "Product") to select all the products listed on the page. Some new options will pop up — click on "Edit Variants".
Step 4: The previous step takes you to the Bulk Editor page. From here, you can add a column for prices (if it's not there already) for editing. Click on the "Add Fields" button and select "Price".
Step 5: A new column appears showing the prices for the products listed on the page. Click on the price of the first one, then hold the "Shift" key on your keyboard.
Start pressing the down arrow key on your keyboard until you have all the prices selected on the page and key in the new price (It will be automatically duplicated for all cells selected), then click on the "Save" button.
Important: Make sure that you wait for the process to finish completely (denoted by a checkmark on the left of each product) before you exit out or proceed to the next page.