The battery's capacity is significantly reduced

[Larry]

Please can you inform me how I improve capacity or put a new one in. MacBook Air (13-inch, 2017) 11.1 Big Sur.

[Xairbusdriver]

1. What have you tried?

2. What have your searches suggested?

3. How have you verified a capacity Loss?

[Larry]

I held the Option and clicked the battery icon in the top right corner to reveal the battery condition, and I just wondered there was another way to remedy this?

[Xairbusdriver]

I held the Option and clicked the battery icon in the top right corner to reveal the battery condition

OK. That reports an estimated charge remaining. It is not an indication of "capacity". Your original post asked how to "improve capacity". The capacity is pretty much built into the battery at the battery factory. It does decline with age, but there is no way I know of to "improve" it. Recharging is not "improving capacity".

If you are asking how to make a battery "show" a specific indication of 'power' for longer periods of time, you must simply use it less. That 'battery power indicator' is basically like the fuel tank gauge on your car. You can get a fairly accurate estimate on how far you can drive with the remaining fuel. But you can only 'recharge' the tank until it is full. You have no control over it's capacity.

I just wondered [if] there was another way to remedy this?

I don't know exactly what you are wanting to "remedy". Answers to questions 1, 2 & 3 in post #1 might reveal a clue.

[Paddy]

Larry, go to About This Mac->System Report->Power and the section you want to look at (or copy and paste here) will look like this (this is from my 2019 15" MBP):

Charge Information:
  Charge Remaining (mAh):   6058
  Fully Charged:   Yes
  Charging:   No
  Full Charge Capacity (mAh):   6297
  Health Information:
  Cycle Count:   60
  Condition:   Normal

A new 2017 13" MBA would likely have around 4596 mAh of battery capacity.

Does the battery condition say "replace soon" or "replace now"? Does the MBA die suddenly with no warning when there is still more than 10% charge left (ostensibly)? If the latter - get it replaced. Or replace it yourself - OWC has nice larger capacity batteries you can install.

https://www.ifixit.com/Guide/MacBook+Air+13-Inch+Early+2017+Battery+Replacement/135927

https://eshop.macsales.com/item/NewerTech/BAP13MBA60/

Or get Apple to do it (though they won't be using the larger capacity battery OWC offers) - but at least if anything gets screwed up, it's on them, not you.

https://support.apple.com/mac/repair/service