I am trying to set up restaurant inventory and calculate cost of goods sold using Quickbooks online. Any suggestions on the accounts I should use to enter purchases and then to adjust for ending inventory each month?

don't set up inventory for a restaurant, instead use the periodic inventory method

There are two ways to do periodic inventory, choose one and stick with it, you can not mix and match

1. (my preference) Create an asset account called purchases and post all purchases of item for resale to that account. Periodically, weekly, monthly, etc value the inventory on hand, subtract that value from the amount shown in the purchases account and do a journal entry for the answer to the subtraction
debit COGS for that value
credit purchases for that value

OR

2. Post all purchases to COGS. Periodically, but at least at the end of the year, you value the inventory on hand and do a journal entry.
debit the asset purchases account for that value
credit COGS for that value

Print the P&L
then reverse the journal entry
debit COGS for that same value
credit the asset purchases account for that value

This last journal entry, moves the value of what was on hand at the end of year back to COGS so the cost will be counted against the new year sales.

@Bosskoss 

There is a restaurant management app supporting QuickBooks and integrate with many POS solution for restaurant. Some of the features are inventory management, food cost management, and recipe management. Send your business email address in a private message to let us introduce you to them. 

Hi

#There is a restaurant management app supporting QuickBooks and integrate with many POS solution for restaurant. Some of the features are inventory management, food cost management, and recipe management.

Can you send me your suggestion software to my email [email address removed] because currently i'm uploading sales report from Storehub to Quickbook and still need to update manually some information and figure to the report.

Thanks and regards