Revise existing custom WordPress plugin

We have a custom WordPress plugin which was made by a dev who isn't available anymore.

The plugin has one main function, to display product variation swatches at any amount in a box that appears from the bottom of the browser once the "select colour" button has been pressed, allowing the customer to choose / search whichever colour of product they want to purchase, click on it and then able to add to basket.

Issue that has arose, which was overlooked when the plugin was developed is the FCP (First contentful paint), when a product has many variations, in this example over 1,000 the browser is loading them with all other page resources.

I would like the plugin to be modified to only load the swatches in either a 'lazy load' format or another method that you, as a developer, can recommend. This way, the page load & FCP will dramatically reduce as it will only load once the request on pressing the button is there.

Some of you may have already put your proposal through on a previous job listing, the job descriptions was somewhat vague and i've been getting a variation of prices. This job post is to make it clear what i need so that i'm able to receive accurate prices.