Being behind is normal. Most new clients come in exactly here. The way out is a sequence, not a weekend.
Bank and credit-card statements for every month, for every account the business touched. Download the PDFs or give your bookkeeper online read-only access. Statements are the backbone; receipts are the detail.
Usually January 1 of the earliest year that still needs a tax return. Older than that, ask your preparer whether it matters before you spend money rebuilding it.
Each month: every statement line gets a category, deposits get matched to invoices or marked as owner money, and the ending balance is reconciled to the statement. A month that reconciles is done; move on.
Lines nobody can identify go on a short list for you to answer in one sitting. Guessing categories is how clean-up work gets redone.
We quote catch-up by the month of records, after seeing one statement, so you know the total before any work starts. Then monthly bookkeeping keeps you from being here again.
Flat monthly price, quoted on a 20-minute call.