How do you add historical aggregate transactions for a year or quarter?

Did your contributions all buy one security, and the matching contributions buy the same or one different security? Do you have the share balances for each period?

If so, you can enter your approximate activity as follows:

Say B1 is the share balance for a security at the end of Q1, B2 is the balance at the end of Q2, and C2 is the contribution for that security during Q2.

Then at the middle of Q2, enter a purchase of B2-B1 shares for C2 total. Let Quicken calculate the average cost per share. Enter the ending share price for the security. Check that the security value for the account is correct and that the cash balance is zero.

Or if you care mainly about the account balance and not the performance of the account and the securities in it, you can put the account in Simple mode and just enter the ending cash balance and the number of shares. To switch to Simple mode, go to Edit > Preferences > Investing and make sure Simple mode is enabled. Then go to the account, click on the gar at the top right, select Edit Account Details, and select Simple mode.

In Simple mode for an offline account, you will see a dashboard instead of the detailed transaction list. At the end of each quarter, click on the gear at the top right of the account and enter the share balances, cash balance, and security prices. If the securities in the account are pulicly traded, you can still update the quotes without entering the prices manually.

Normally the contributions to the account from your paycheck and any company match would add to the cash in the account. The most complete way to handle this would be to enter Buy transactions. These will use the cash to buy the right number of shares to match your ending balance. You would enter these transactions in the middle of the period because you don't know the exact timing of the transactions. The NAV the FI provides will be the price at the end of the period.

If you just do an Update share balance, the share balance will change but the cash will not be used up. You could also update the cash balance to get rid of that if you want, so you end each period with the correct number of shares, the correct account balance, and zero cash. That is essentially what Quicken does in Simple mode.

It's up to you which method to use. The one I described will take a little extra work, but will give a more accurate picture of what happened to your account over time.