How to drop foreign key which is not defined as constraint

CREATECOLUMNTABLE."USERS" ("user_id"INTEGER CS_INT GENERATED BYDEFAULTASIDENTITYNOTNULL ,

   "email"NVARCHAR(80) NOTNULL ,

   "password"NVARCHAR(50) NOTNULL ,

   "is_active"INTEGER CS_INT DEFAULT 1,

   PRIMARYKEY ("user_id")) UNLOADPRIORITY 5 AUTO MERGE

CREATECOLUMNTABLE."USERSEXTRA" ("user_id"INTEGER CS_INT NOTNULL ,

   "first_name"NVARCHAR(25) NOTNULL ,

   "last_name"NVARCHAR(25) NOTNULL ,

   "profile_image"BLOB MEMORY THRESHOLD 1000,

   "mobile"NVARCHAR(20),

   "create_date" LONGDATE CS_LONGDATE,

   "last_login_date" LONGDATE CS_LONGDATE) UNLOADPRIORITY 5 AUTO MERGE

;

ALTERTABLE."USERSEXTRA"ADDFOREIGNKEY ( "user_id" ) REFERENCES."USERS" ("user_id") ONUPDATECASCADEONDELETECASCADE