How to encrypt and decrypt a transposition cipher?
For Decryption Process, use the reverse of encryption process.
I think you are using a wrong table format. The table should be 4*3 instead of 3*4. Now, Write your encrypted text column by column(4 rows and 3 cols). It will be like this.

e h l

o l _

h t e

e r x

Now, Apply the decryption key of key 2 1 3. The decryption key will be the same.

2 1 3

| | |

2 1 3

Now, arrange the message in columns from above by making necessary transformations. The table will become,

h e l

l o _

t h e

r e x

Now, Read row by row. Your Message will be

hello there


Remember, For decryption, apply the same process for encryption in reverse order.
Hope that helps. :)