What could be the Cipher String to add 3DES Cipher to SSL Profile ?

3DES is no longer included in "DEAULT" on v13.1, unlike v11.6.3. It is still listed in 'NATIVE', though:

 tmm --clientciphers 'NATIVE' | grep CBC3
98: 49170  ECDHE-RSA-DES-CBC3-SHA           168  TLS1    Native  DES       SHA     ECDHE_RSA 
99: 49170  ECDHE-RSA-DES-CBC3-SHA           168  TLS1.1  Native  DES       SHA     ECDHE_RSA 
100: 49170  ECDHE-RSA-DES-CBC3-SHA           168  TLS1.2  Native  DES       SHA     ECDHE_RSA 
101: 49165  ECDH-RSA-DES-CBC3-SHA            168  TLS1    Native  DES       SHA     ECDH_RSA  
102: 49165  ECDH-RSA-DES-CBC3-SHA            168  TLS1.1  Native  DES       SHA     ECDH_RSA  
103: 49165  ECDH-RSA-DES-CBC3-SHA            168  TLS1.2  Native  DES       SHA     ECDH_RSA  
104:    10  DES-CBC3-SHA                     168  TLS1    Native  DES       SHA     RSA       
105:    10  DES-CBC3-SHA                     168  TLS1.1  Native  DES       SHA     RSA       
106:    10  DES-CBC3-SHA                     168  TLS1.2  Native  DES       SHA     RSA       
107:    10  DES-CBC3-SHA                     168  DTLS1   Native  DES       SHA     RSA       
108: 49160  ECDHE-ECDSA-DES-CBC3-SHA         168  TLS1    Native  DES       SHA     ECDHE_ECDSA
109: 49160  ECDHE-ECDSA-DES-CBC3-SHA         168  TLS1.1  Native  DES       SHA     ECDHE_ECDSA
110: 49160  ECDHE-ECDSA-DES-CBC3-SHA         168  TLS1.2  Native  DES       SHA     ECDHE_ECDSA
111: 49155  ECDH-ECDSA-DES-CBC3-SHA          168  TLS1    Native  DES       SHA     ECDH_ECDSA
112: 49155  ECDH-ECDSA-DES-CBC3-SHA          168  TLS1.1  Native  DES       SHA     ECDH_ECDSA
113: 49155  ECDH-ECDSA-DES-CBC3-SHA          168  TLS1.2  Native  DES       SHA     ECDH_ECDSA
114:    22  DHE-RSA-DES-CBC3-SHA             168  TLS1    Native  DES       SHA     EDH/RSA   
115:    22  DHE-RSA-DES-CBC3-SHA             168  TLS1.1  Native  DES       SHA     EDH/RSA   
116:    22  DHE-RSA-DES-CBC3-SHA             168  TLS1.2  Native  DES       SHA     EDH/RSA   
117:    22  DHE-RSA-DES-CBC3-SHA             168  DTLS1   Native  DES       SHA     EDH/RSA   
118:    27  ADH-DES-CBC3-SHA                 168  TLS1    Native  DES       SHA     ADH       

Try this:

 tmm --clientciphers 'DEFAULT:ECDH-RSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:ECDHE-ECDSA-DES-CBC3-SHA' | grep CBC3
56: 49165  ECDH-RSA-DES-CBC3-SHA            168  TLS1    Native  DES       SHA     ECDH_RSA  
57: 49165  ECDH-RSA-DES-CBC3-SHA            168  TLS1.1  Native  DES       SHA     ECDH_RSA  
58: 49165  ECDH-RSA-DES-CBC3-SHA            168  TLS1.2  Native  DES       SHA     ECDH_RSA  
59: 49170  ECDHE-RSA-DES-CBC3-SHA           168  TLS1    Native  DES       SHA     ECDHE_RSA 
60: 49170  ECDHE-RSA-DES-CBC3-SHA           168  TLS1.1  Native  DES       SHA     ECDHE_RSA 
61: 49170  ECDHE-RSA-DES-CBC3-SHA           168  TLS1.2  Native  DES       SHA     ECDHE_RSA 
62: 49160  ECDHE-ECDSA-DES-CBC3-SHA         168  TLS1    Native  DES       SHA     ECDHE_ECDSA
63: 49160  ECDHE-ECDSA-DES-CBC3-SHA         168  TLS1.1  Native  DES       SHA     ECDHE_ECDSA
64: 49160  ECDHE-ECDSA-DES-CBC3-SHA         168  TLS1.2  Native  DES       SHA     ECDHE_ECDSA

DES and 3DES comes under

BulkCrypto

and its already added with DEFAULT(NATIVE) cipher but you can't add

3DES

cipher alone. i believe, will come with the combination of example: RSA+3DES, ECDHE+3DES, etc.

Did you tried

DEFAULT:+3DES

?

Confirm the F5 version and purpose to use?