Hello, I have a business and I leased new space in 2018. Where do I deduct expenses for improvements/fit up I made to my space in 2018. Total fit up expenses 43,324.

The expenses that you are asking about are usually referred to as "leasehold improvements." They are entered into TurboTax as business assets.

Leasehold improvements are amortizable business assets as the lessee only has the intangible right to use them during the term of the lease. Thus, they are amortized over the term of the lease or the useful life of the asset, whichever is shorter. You may need to separate out the types of assets that make up your total build-out costs: interior walls have a longer useful life than fixtures or carpeting. Leasehold improvements are also subject to first-year write-off under Sec. 179.

Additional useful information may be found in IRS Pub. 946 How To Depreciate Property.