I showed the ways to add pieces to your store using what Bricklink gives us. There are makers of third party software that might make it easier to add pieces. I have tried to use software before it can be difficult to figure out how to use them. This one is called Brickstore. It is available on this website: Brickstore. You can follow the installation instructions on GitHub.
Open Brickstore and this is the main screen. The very first thing that you need to do is log into Bricklink otherwise you can’t add or edit anything in your store. Under the Brickstore tab at the top of your screen go to Preference and then Bricklink
Enter your BL username and password. Make sure that the info is correct. If there is a problem uploading or downloading from your store, this is probably where the problem is. Close off the settings and back to the main screen, first image. Select New and a new screen appears
To do anything on this screen, click on the brick with the green plus sign and another new screen appears.
On the left is all the BL categories. In the middle are all the pictures in the category and on the right are the colors that it is available in if Known Colors is selected. I selected a 2×4 Brick 3001 in orange. In the bottom right you can add your quantity, condition, your locations in the Remarks field and pricing. It is probably easier to leave the pricing blank and just enter your qty, condition and locations and then click add.
I added the same piece in different colors and quantities. Everything you added shows up on the main screen. The price field is red. If you select all the pieces you add you can update to the current prices.
If you click on the $ with the Bricklink Head it will give you pricing options. I am choosing Current Inventory Average and click Ok. The prices will now be filled in. If you are done you can now upload your new inventory to your store. Under File there is the option to upload.
Select the second option Mass Upload to Clipboard. Once selected it will open a new tab in your browser to your Bricklink store
Selecting the Export it will have put everything you added into the clipboard. Click in the big empty rectangle and paste it in.
Once pasted, then click Verify File.
You can check to see if everything is complete and then click verify on the bottom of the screen. Now those pieces are now in your inventory. Next you can use Brickstore to update the prices in your store.