I have some numbers in coloum A
i.e.

5689745864
568789652445
568123658974
5685416859
568436468
56836465765354
56873614367436436
5.6891E+12 - ( some number are getting displayed as, when I change the
format of the coloum to number - the displayed format is
568954125325778246656465465)

What I want is in Coloum B - should have the only first 10 digitsd from
coloum A)

so the result should look like

5689745864
5687896524
5681236589
5685416859
5684364685
5683646576
5687361436
5.6891E+12 should change to 5689541253

One possibility is to put this in A1 and copy down:
=LEFT(TEXT(A1,"#"),10)