404 error pages can be located during a link audit and these errors need to be rectified by re-directing the 404 pages to appropriate ones. If your link audit throws up a few pages then it may be an easy task to rectify, but if there are a huge number of 404 pages, you first need to decide on which pages are actually important before you take action.
There are several crucial metrics such as landing page visits, backlinks, social metrics, etc., to consider while deciding on which 404 pages you need to save. There are several tools such as Google Webmaster Tools [GWT] and Screaming Frog, among others that can help you locate 404 pages.
For locating 404 pages in GWT, you need to click on Health, Crawl Errors, URL Errors, Web or Mobile: Not Found, and then on Download. You can save this file in the form of .xlsx once you remove everything from the csv download other than the 404 URL list.
Screaming Frog requires you to click on Response Codes, Filter: Client Error (4xx), and finally on Export. For WordPress sites, Broken Link Checker is a useful tool that makes it easy to identify and remove links, although it can put a load on your server and can cause linking issues if used carelessly.
You can now view all landing pages displayed at the bottom of your report. For landing pages that number over 500, you will need special skills to increase the number of rows. You will now need to get backlinks by using your chosen tool. You can easily get online help in using Google Webmaster Tools as well as for other tools such as Ahrefs and Majestic.
You can finally begin viewing all your 404 pages and rectify important URL issues by adding or deleting http:// as per your specific needs. You can use VLOOKUPs in MS Excel to combine all desired metrics. You must remember to format the dataset in the form of a table to help you sort your data by backlinks, landing page visits, page authority, or any other data that you include in your dataset.
The above method will help you identify and save important 404 pages from a sea of such pages during a link audit.