Make another column rounding the y-values to thousands and chart this data
If first y-value is in B2 use in C2 =ROUND(B2,-3)
Select all the x-values; hold CTRL key and select all the new y-values; make
chart
best wishes
If you don't want to change the values, but only the display, select and
right-click the data, choose format, then click on Number, and choose a
number tab like one of these
0,
0,k
The comma drops the last three digits, displaying the thousands rounded
to the nearest thousand, but the underlying values are unchanged.