The easiest thing to do would be to buy the solution already made, whcih is economical if you don't need a very large amount.

Starting from the solid, it would have been easier if you had bought Tris base instead of Tris-HCl. Then you could have adjusted the pH to 8 using HCl.

Starting from Tris-HCl, to get to pH 8 you have to add base. You could use NaOH, but then you would have a solution containing Tris and NaCl. A better method would be to mix a solution of Tris-HCl with an equimolar solution of Tris base. So, you should buy some Tris base.

Prepare 1 M stock solutions of Tris-HCl and Tris base. If there is a pH meter available, check the manufacturer's information on the pH electrode to make sure it is Tris-compatible. Not all of them are. If it is, calibrate the pH meter using commercially-prepared standard buffers at pH 7 and 10.

(If there is no pH meter available

You will need a beaker, a magnetic stirrer and a stir bar. Half fill the beaker with 1 M Tris base, start stirring, and start measuring the pH. Gradually add the 1M Tris-HCl until the pH drops to 8. (You could also add the Tris base solution to the Tris-HCl solution.) Since both solutions are already 1 M Tris, the mixture will also be a t 1 M.

The pH of Tris solutions is significantly affected by temperature, so the ideal procedure would be to measure the pH at the temperature at which the solution is going to be used. Furthermore, the pH will change when the solution is diluted, so it is a good idea to prepare a stock solution that is close to the final concentration at which the buffer will be used., if a precise value of pH is required.

If you don't have a pH meter available, you could use pH strips, but they are not very accurate and can only get you to within about half a pH unit.

Or, you could try using this calculator. I don't know how accurate it is, but someone else recommended it 2 years ago. (https://www.researchgate.net/post/How-to-calculate-mass-of-dry-Tris-base-Tris-HCl-to-dissolve-to-give-a-buffer-with-desired-concentration)

https://www.geneandcell.com/pages/hasselbalch