I'm glad that you've asked this question, since it's often overlooked and tax policy has changed over the years regarding this topic. The manner in which a business owner pays for a Medicare supplemental policy can save real money in taxes.
The short answer is that the business should pay for Medicare supplemental insurance (i.e., Medicare Part B premiums), which typically ranges from $1,200 to $3,120. The premiums are deducted via line 29 of your form 1040 since you're likely a pass-through entity as a single-member LLC. This is referenced in Section 162(l) of the Internal Revenue Code. Please note that it is especially important that you follow this tax treatment since deducting self-employed insurance premiums can also actually lower your self-employment tax.
If you didn't claim this deduction in years past, you can certainly amend your tax return for those years that fall within the statute of limitations. If the Medicare supplemental policy was treated as a personal expense, it would be deductible only if it and other related expenses exceeded the 7.5% of adjusted gross income floor set by the IRS.