Easy in perl
perl -pe 's-(\d+.?\d*)-($1/1000)-ge' file
add
tube
3033.303 2998.20695111 106.1801625
0.060325 6.22260621
y
0 0
0
add
cube
3027.18924332 3032.17578955 114.50875
0.1689 6.17076909
y
0 0
0
0
solved Unit conversion from mm to m in text file with text and numbers