First you change the cm to metres. To do that, divide by 100. So you would have 0.001 m.
F = Ke
Where K is spring constant, F is force and e is extension.
To get force, you need to use the formula W = mg, where W is weight (force), m is mass (kg) and g is gravitational constant (usually 10). So to find force;
W = mg
W = 1 × 10
W = 10N
To find K;
F = Ke
10 = K × 0.001
10 = 0.001 K
K = 10 ÷ 0.001
K = 10000 N/m
Hope this helps!