Find z such that 5.0% of the standard normal curve lies to the left of z.
Don't know if you are using 1970s kind of tables or graphs, but ....
find .05 in the main body of the table.
h tt p://www.z-table.com/
(delete the spaces obviously)
I see .0505 with a z of -1.64 and .0495 with a z of -1.65
so I would pick half way between as -1.645
OR
open a new page, enter the following into the URL, (delete the 2 spaces
at the front again)
h tt ps://davidmlane.com/normal.html
click on "value from an area"
enter .05 in the box labeled "area"
the mean and SD should show as 0 and 1
in the "results" click on "below" and you should get
-1.645