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What you've written is extremely ambiguous. I have to guess what you mean and answer based on my guess. I am, therefore, assuming that what you are asking is this:

"The login button generated by SocialLogin plugin implementing the Login with Amazon feature includes an IMG tag pointing to the Amazon logo image file https://ev-cables.co.uk/media/plg_sociallogin_amazon/images/amazon.png. The IMG tag has an alt attribute, but it's empty. I am using <Some Accessibility Checker Tool> which complains about this empty alt attribute, saying <something which does not matter>. Is there a quick fix for this?"

I take accessibility very seriously. All of us will become disabled to an extent as we're growing older.

The empty alt tag is a deliberate choice which avoids an accessibility issue for users with visual impairments.

The Amazon logo on the login button is a decorative image as per the W3C Web Accessibility Initiative:

Decorative images don’t add information to the content of a page. For example, the information provided by the image might already be given using adjacent text, or the image might be included to make the website more visually attractive.

This is indeed the case with the Amazon logo on the button labelled as "Login with Amazon". The logo represents the word "Amazon", which exists as text in the same context (button element). Its placement is solely for compliance with the brand guidelines of Amazon Inc, i.e. only there for visual attractiveness reasons. It does not provide any information which is not already present as text.

As per the WAI page I linked to, we must use an empty alt tag in this image. Using a non-empty alt tag, or using no alt tag, would be a problem. Here's the direct quote:

In these cases, a null (empty) alt text should be provided (alt="") so that they can be ignored by assistive technologies, such as screen readers. Text values for these types of images would add audible clutter to screen reader output or could distract users if the topic is different from that in adjacent text. Leaving out the alt attribute is also not an option because when it is not provided, some screen readers will announce the file name of the image instead.

Indeed, had we put the alt attribute content "Amazon logo" the screen reader would've announced "Button. Amazon logo. Login with Amazon." which is not just confusing, it's outright stupid. Using no alt tag might make some screen readers announce this similar to "Button. Image. Login with Amazon." which is confusing, as it makes the user wonder what the image is (they will of course understand it's just a logo, but the experience is suboptimal to say the least). With an empty alt tag the screen reader announces the element as something similar to "Button. Login with Amazon." which is precisely what we need to convey the type and reason of existence of this element.

Some accessibility checker tools, unfortunately, conflate empty alt attributes with no alt attributes even though they are both functionally and semantically different. This leads to erroneous reports of accessibility errors when, in fact, the choice of an empty alt tag was a conscious effort to explicitly avoid an accessibility error.

I hope this helps.