Go to Inventory -> All and on the rightmost side, near the Create Product button, you will see the white Import button.
Before Updating Inventory you need to download an existing .csv inventory file by simply exporting it. To do that, simply press on the Export button, and then Export All or Export Filtered.
Note: downloaded files will be found in the Reports section.
Open the now downloaded sheet and change wanted fields. After you're done, simply press Save and go back to Multiorders Inventory page.
Note: Product Name, SKU, Images, Marketplace Id, and Multiorders Id can not be changed.
In here, press Import and then press Update, Select Update stock and Update price if you prefer to, then press Choose Sheet to find the .csv file you have just saved and press Import.
Depending on the volume of inventory this could take a few seconds or a few minutes. If however the upload has completed and the updated inventory did not appear, there may be a problem in the way you filled out the .csv sheet.
Contact customer service in this case and they will be able to fix your sheet.