Your client wants to improve the results of your ads, so they suggest to increase...

The four main factors that affect your ad in an auction are the following:

Advertiser Bid: How much you value the results you are trying to obtain.

Estimated Action Rates: How likely Facebook thinks a given person will take action on your ads. Estimated action rates are based on the person you're reaching historical data and your ad's historical data performance.

Ad quality: Basically this comes down to your images or creative. The better the ad image, video or design, the more appealing it will be to your target audience; thus, increasing the ad quality.

Relevance: If ads are getting negative feedback or are not getting actions, your relevance will be much lower.

Ad relevance diagnostics aren't inputs into the ad auction:

Quality Ranking: How your ad's perceived quality compared to ads competing for the same audience.

Engagement Rate Ranking: How your ad's expected engagement rate compared to ads competing for the same audience.

Conversion Rate Ranking: How your ad's expected conversion rate compared to ads with the same optimization goal competing for the same audience.

Facebook uses user value, not any of the ad relevance diagnostics in calculating Total Value. Just keep in mind that the Relevance Diagnostics is an output of all of the metrics above; NOT an input.  

Frequency is only a metric as a result of your ads and relationship between reach and impressions.